1. Field of the Invention
The present invention relates to an automatic transmission mounted on a vehicle of a passenger car, for example, and specifically, to a hydraulic control system and a control system therefor.
2. Description of the Related Art
Generally, an automatic transmission having a reverse inhibit function not to establish a reverse gear even when a shift lever is operated to a reverse range while a vehicle travels forward at a predetermined or higher speed is widely known. However, in the automatic transmission having the reverse inhibit function, particular valves of a hydraulic control system are controlled not to establish the reverse gear, and accordingly, for example, when the valves lock up in the reverse inhibit state for any reason, the reverse gear may not be established.
On this account, in related art, an automatic transmission adapted to achieve a reverse gear even in the case where particular valves lock up in the reverse inhibit state has been devised (see JP-A-2009-180339).
The automatic transmission in JP-A-2001-4018 includes a reverse sequence valve 4400 that engages and stops a B2 brake 3620 and a B3 brake 3600 to establish a reverse gear and selectively supplies a reverse range pressure and a control pressure of a linear solenoid valve SL4 to the B3 brake 3600 as an engagement pressure, and a B2 control valve 4500 that switches a hydraulic pressure supplied to the B2 brake 3620. Further, by connecting an output port 4406 of the reverse sequence valve 4400 that may communicate with a drain port EX and an input port 4505 of the B2 control valve 4500, the engagement pressure of the B3 brake 3630 is drained from a drain port of the linear solenoid valve SL4 at reverse inhibit and the engagement pressure of the B2 brake 3620 is drained from a drain port EX of the reverse sequence valve 4400 via the input port 4505 and the output port 4406 (see FIG. 7 of JP-A-2001-4018).
Further, the reverse range pressure is input to two input ports 4401, 4403 of a reverse sequence valve 4400 that may communicate with the hydraulic servo of the B3 brake or the output port 4406, and thus, as shown in FIGS. 8 and 9 of the JP-A-2001-4018, even in the case where either the B2 control valve 4500 or the reverse sequence valve 4400 lock up in the reverse inhibit position, the reverse range pressure or the control pressure of the linear solenoid valve SL4 may be supplied to the B2 and B3 brakes 3620, 3630 as the engagement pressure, and the reverse gear may be established.